State of Charge Information for a Wireless Power Transmitting Device

ABSTRACT

A wireless power system may include power transmitting devices, power receiving devices, and power transmitting and receiving devices. During a configuration phase (e.g., when placed adjacent to another device), a battery-powered transmitting device may transmit information to the additional device that identifies a presence of the battery in the transmitting device. The battery-powered transmitting device may periodically report its state of charge to a power receiving device using in-band communication. The battery-powered transmitting device may report its state of charge before a power transfer phase (e.g., in the configuration phase) or during the power transfer phase. The battery-powered transmitting device may report its state of charge to the power receiving device in response to a state of charge query from the power receiving device. The power receiving device may display the state of charge of the battery of the power transmitting device.

This application is a continuation of U.S. patent application Ser. No.17/100,598, filed Nov. 20, 2020, which claims the benefit of provisionalpatent application No. 63/047,797, filed Jul. 2, 2020, and provisionalpatent application No. 63/047,779, filed Jul. 2, 2020, which are herebyincorporated by reference herein in their entireties.

FIELD

This relates generally to power systems, and, more particularly, towireless power systems for charging electronic devices.

BACKGROUND

In a wireless charging system, a wireless power transmitting device suchas a charging mat wirelessly transmits power to a wireless powerreceiving device such as a portable electronic device. The wirelesspower receiving device has a coil and rectifier circuitry. The coilreceives alternating-current wireless power signals from the wirelesscharging mat. The rectifier circuitry converts the received signals intodirect-current power.

SUMMARY

A wireless power system may include one or more wireless powertransmitting devices, one or more wireless power receiving devices, andone or more wireless power transmitting and receiving devices. Thewireless power transmitting device may include a coil and wireless powertransmitting circuitry coupled to the coil. The wireless powertransmitting circuitry may be configured to transmit wireless powersignals with the coil. The wireless power receiving device may include acoil that is configured to receive wireless power signals from thewireless power transmitting device and rectifier circuitry that isconfigured to convert the wireless power signals to direct currentpower. The wireless power transmitting and receiving device may includeat least one coil and both wireless power transmitting circuitry andwireless power receiving circuitry.

Power transmitting and receiving devices (as well as some dedicatedpower transmitting devices) may include batteries. These battery-powereddevices are capable of operating in a power transmitting mode and may bereferred to as battery-powered transmitting devices. During aconfiguration phase (e.g., when placed adjacent to another device), thebattery-powered transmitting devices may transmit information to theadditional device that identifies a presence of the battery in thetransmitting device.

The battery-powered transmitting device may periodically report itsstate of charge to a power receiving device using in-band communication.The battery-powered transmitting device may report its state of chargebefore a power transfer phase (e.g., in the configuration phase) orduring the power transfer phase. In some cases, the battery-poweredtransmitting device may report its state of charge to the powerreceiving device in response to a state of charge query from the powerreceiving device.

The power receiving device may display the state of charge of thebattery of the power transmitting device. If the state of charge of thebattery of the power transmitting device drops below a threshold, thepower receiving device may notify the user that wireless chargingoperations will imminently end. Either the power transmitting device orthe power receiving device may initiate a role swap based on the stateof charge of the battery of the power transmitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative wireless power systemin accordance with an embodiment.

FIG. 2 is a circuit diagram of illustrative wireless power transmittingand receiving circuitry in accordance with an embodiment.

FIG. 3 is a state diagram of illustrative modes of operation for awireless power transmitting and receiving device in accordance with anembodiment.

FIGS. 4A and 4B are a timing diagram showing how a default powerreceiving device may be placed adjacent to a default power transmittingdevice and ultimately swap roles in accordance with an embodiment.

FIG. 5 is a timing diagram showing how a default power receiving devicemay be placed adjacent to another power receiving device and ultimatelyswitch to a power transmitting mode in accordance with an embodiment.

FIG. 6 is a diagram of an illustrative packet that may be used to sendrole swap capability information and other charging information from adevice in a power receiving mode or a power transmitting mode inaccordance with an embodiment.

FIG. 7 is a diagram of an illustrative packet that may be used to send arole swap request from a device in a power receiving mode or a powertransmitting mode in accordance with an embodiment.

FIG. 8 is a timing diagram showing how a power role swap may occurbefore a power transfer phase in accordance with an embodiment.

FIG. 9 is a timing diagram showing how a power swap may occur during apower transfer phase in accordance with an embodiment.

FIG. 10 is a flowchart of illustrative method steps for operating apower transmitting and receiving device in accordance with anembodiment.

FIG. 11 is a top view of an illustrative charging system showing how apower receiving device may display battery charge status information forboth the power receiving device and an adjacent power transmittingdevice in accordance with an embodiment.

FIG. 12 is a timing diagram showing how a power receiving device maysend a state of charge query to a power transmitting device andsubsequently receive the state of charge of a battery in the powertransmitting device in accordance with an embodiment.

FIG. 13 is a flowchart of illustrative method steps for operating apower transmitting device that transmits its state of charge to a powerreceiving device during wireless charging in accordance with anembodiment.

FIG. 14 is a flowchart of illustrative method steps for operating apower receiving device that receives a message indicative of the stateof charge of a battery of a power transmitting device during wirelesscharging in accordance with an embodiment.

DETAILED DESCRIPTION

A wireless power system may include one or more electronic devices thattransmit wireless power, one or more electronic devices that receivewireless power, and one or more electronic devices that both transmitand receive wireless power. The wireless power transmitting device maybe a wireless charging mat or wireless charging puck, as examples. Thewireless power receiving device may be a device such as a wrist watch,cellular telephone, tablet computer, laptop computer, or otherelectronic equipment, as examples. The wireless power transmitting andreceiving device may be an electronic device case (e.g., a case for acellular telephone) or other type of electronic device. The wirelesspower transmitting device may wirelessly transmit power to a wirelesspower receiving device. The wireless power receiving device uses powerfrom the wireless power transmitting device for powering the device andfor charging an internal battery.

Wireless power is transmitted from the wireless power transmittingdevice to the wireless power receiving device using one or more wirelesspower transmitting coils. The wireless power receiving device has one ormore wireless power receiving coils coupled to rectifier circuitry thatconverts received wireless power signals into direct-current power.

An illustrative wireless power system (wireless charging system) isshown in FIG. 1 . As shown in FIG. 1 , wireless power system 8 mayinclude one or more wireless power transmitting devices such as wirelesspower transmitting device 12, one or more wireless power receivingdevices such as wireless power receiving device 24, and one or moreelectronic devices capable of both transmitting and receiving wirelesspower such as wireless power transmitting and receiving device 18. Itshould be understood that one or more of each type of device may bepresent in the wireless power system at any given time, with devicesbeing added and removed from the system in a fluid manner. Additionally,one or more devices may switch between tethered (where the devicereceives power from a wall outlet or other power source) and untethered(where the device battery is used to power the device) states. Thefunction of power transmitting and receiving device 18 may changedepending upon the arrangement of the system at a given time. A powertransmitting and receiving device may only transmit power in somescenarios, may only receive power in some scenarios, and may bothtransmit and receive power in some scenarios. A power transmittingdevice 12 may transmit power directly to a power receiving device 24 insome scenarios. In other scenarios, power transmitting device 12 maytransmit power to a power transmitting and receiving device 18, whichthen transmits the power to power receiving device 24. The functionalityof each device and inductive coupling between each device within thesystem may be updated as devices are added to and removed from thesystem.

Wireless power transmitting device 12 includes control circuitry 16.Wireless power receiving device 24 includes control circuitry 30.Control circuitry 30 includes measurement circuitry 43 and wirelesstransceiver circuitry 46. Wireless power transmitting and receivingdevice 18 includes control circuitry 78. Control circuitry in system 8such as control circuitry 16, control circuitry 30, and controlcircuitry 78 is used in controlling the operation of system 8. Thiscontrol circuitry may include processing circuitry associated withmicroprocessors, power management units, baseband processors, digitalsignal processors, microcontrollers, and/or application-specificintegrated circuits with processing circuits. The processing circuitryimplements desired control and communications features in devices 12,18, and 24. For example, the processing circuitry may be used inselecting coils, determining power transmission levels, processingsensor data and other data to detect foreign objects and perform othertasks, processing user input, handling negotiations between devices 12,18, and 24, sending and receiving in-band and out-of-band data, makingmeasurements, and otherwise controlling the operation of system 8.

Control circuitry in system 8 may be configured to perform operations insystem 8 using hardware (e.g., dedicated hardware or circuitry),firmware and/or software. Software code for performing operations insystem 8 is stored on non-transitory computer readable storage media(e.g., tangible computer readable storage media) in control circuitry16, 30, and/or 78. The software code may sometimes be referred to assoftware, data, program instructions, instructions, or code. Thenon-transitory computer readable storage media may include non-volatilememory such as non-volatile random-access memory (NVRAM), one or morehard drives (e.g., magnetic drives or solid state drives), one or moreremovable flash drives or other removable media, or the like. Softwarestored on the non-transitory computer readable storage media may beexecuted on the processing circuitry of control circuitry 16, 30, and/or78. The processing circuitry may include application-specific integratedcircuits with processing circuitry, one or more microprocessors, acentral processing unit (CPU) or other processing circuitry.

Power transmitting device 12 may be a stand-alone power adapter (e.g., awireless charging mat or charging puck that includes power adaptercircuitry), may be a wireless charging mat or puck that is coupled to apower adapter or other equipment by a cable, may be a portable device,may be equipment that has been incorporated into furniture, a vehicle,or other system, may be a removable battery case, or may be otherwireless power transfer equipment. Illustrative configurations in whichwireless power transmitting device 12 is a wireless charging mat or puckare sometimes described herein as an example.

Power receiving device 24 may be a portable electronic device such as awrist watch, a cellular telephone, a laptop computer, a tablet computer,an accessory such as an earbud, or other electronic equipment. Powertransmitting device 12 may be coupled to a wall outlet (e.g., analternating current power source), may have a battery 32 for supplyingpower, and/or may have another source of power. Power transmittingdevice 12 may have an alternating-current (AC) to direct-current (DC)power converter such as AC-DC power converter 14 for converting AC powerfrom a wall outlet or other power source into DC power. DC power may beused to power control circuitry 16. During operation, a controller incontrol circuitry 16 uses power transmitting circuitry 52 to transmitwireless power to power receiving circuitry 54 of device 24. Forsimplicity, an example is described herein of power transmitting device12 transmitting wireless power to power receiving device 24. However, itshould be understood that a power transmitting and receiving device 18may substitute for one or both of the power transmitting device and thepower receiving device during wireless power transfer operations.

Power transmitting circuitry 52 may have switching circuitry (e.g.,inverter circuitry 61 formed from transistors) that is turned on and offbased on control signals provided by control circuitry 16 to create ACcurrent signals through one or more wireless power transmitting coilssuch as wireless power transmitting coil(s) 36. These coil drive signalscause coil(s) 36 to transmit wireless power. Coils 36 may be arranged ina planar coil array or may be arranged to form a cluster of coils. Insome arrangements, device 12 (e.g., a charging mat, puck, etc.) may haveonly a single coil. In other arrangements, a wireless charging devicemay have multiple coils (e.g., two or more coils, 5-10 coils, at least10 coils, 10-30 coils, fewer than 35 coils, fewer than 25 coils, orother suitable number of coils).

As the AC currents pass through one or more coils 36,alternating-current electromagnetic (e.g., magnetic) fields (wirelesspower signals 44) are produced that are received by one or morecorresponding receiver coils such as coil(s) 48 in power receivingdevice 24. In other words, one or more of coils 36 is inductivelycoupled to one or more of coils 48. Device 24 may have a single coil 48,at least two coils 48, at least three coils 48, at least four coils 48,or other suitable number of coils 48. When the alternating-currentelectromagnetic fields are received by coil(s) 48, correspondingalternating-current currents are induced in coil(s) 48. The AC signalsthat are used in transmitting wireless power may have any suitablefrequency (e.g., 100-250 kHz, etc.). Rectifier circuitry such asrectifier circuitry 50, which contains rectifying components such assynchronous rectification metal-oxide-semiconductor transistors arrangedin a bridge network, converts received AC signals (receivedalternating-current signals associated with electromagnetic signals 44)from one or more coils 48 into DC voltage signals for powering device24.

The DC voltage produced by rectifier circuitry 50 (sometime referred toas rectifier output voltage Vrect) can be used in charging a batterysuch as battery 58 and can be used in powering other components indevice 24. For example, device 24 may include input-output devices 56.Input-output devices 56 may include input devices for gathering userinput and/or making environmental measurements and may include outputdevices for providing a user with output. As an example, input-outputdevices 56 may include a display (screen) for creating visual output, aspeaker for presenting output as audio signals, light-emitting diodestatus indicator lights and other light-emitting components for emittinglight that provides a user with status information and/or otherinformation, haptic devices for generating vibrations and other hapticoutput, and/or other output devices. Input-output devices 56 may alsoinclude sensors for gathering input from a user and/or for makingmeasurements of the surroundings of system 8. Illustrative sensors thatmay be included in input-output devices 56 include three-dimensionalsensors (e.g., three-dimensional image sensors such as structured lightsensors that emit beams of light and that use two-dimensional digitalimage sensors to gather image data for three-dimensional images fromlight spots that are produced when a target is illuminated by the beamsof light, binocular three-dimensional image sensors that gatherthree-dimensional images using two or more cameras in a binocularimaging arrangement, three-dimensional lidar (light detection andranging) sensors, three-dimensional radio-frequency sensors, or othersensors that gather three-dimensional image data), cameras (e.g.,infrared and/or visible cameras with respective infrared and/or visibledigital image sensors and/or ultraviolet light cameras), gaze trackingsensors (e.g., a gaze tracking system based on an image sensor and, ifdesired, a light source that emits one or more beams of light that aretracked using the image sensor after reflecting from a user's eyes),touch sensors, buttons, capacitive proximity sensors, light-based(optical) proximity sensors such as infrared proximity sensors, otherproximity sensors, force sensors, sensors such as contact sensors basedon switches, gas sensors, pressure sensors, moisture sensors, magneticsensors, audio sensors (microphones), ambient light sensors, opticalsensors for making spectral measurements and other measurements ontarget objects (e.g., by emitting light and measuring reflected light),microphones for gathering voice commands and other audio input, distancesensors, motion, position, and/or orientation sensors that areconfigured to gather information on motion, position, and/or orientation(e.g., accelerometers, gyroscopes, compasses, and/or inertialmeasurement units that include all of these sensors or a subset of oneor two of these sensors), sensors such as buttons that detect buttonpress input, joysticks with sensors that detect joystick movement,keyboards, and/or other sensors. Device 12 may optionally have one ormore input-output devices 70 (e.g., input devices and/or output devicesof the type described in connection with input-output devices 56).Device 18 may optionally have one or more input-output devices 92 (e.g.,input devices and/or output devices of the type described in connectionwith input-output devices 56).

Device 12, device 18, and/or device 24 may communicate wirelessly usingin-band or out-of-band communications. Device 12 may, for example, havewireless transceiver circuitry 40 that wirelessly transmits out-of-bandsignals (e.g., to device 18 or device 24) using an antenna. Wirelesstransceiver circuitry 40 may be used to wirelessly receive out-of-bandsignals from device 18 or 24 using the antenna. Device 24 may havewireless transceiver circuitry 46 that transmits out-of-band signals.Receiver circuitry in wireless transceiver 46 may use an antenna toreceive out-of-band signals. Device 18 may have wireless transceivercircuitry 80 that transmits out-of-band signals. Receiver circuitry inwireless transceiver 80 may use an antenna to receive out-of-bandsignals. Wireless transceiver circuitry 40, 46, and 80 may also be usedfor in-band transmissions between devices 12, 24, and 18 using coils 36,48, and 90.

Frequency-shift keying (FSK) and/or amplitude-shift keying (ASK) may beused to convey in-band data between devices 12, 18, and 24. Power may beconveyed wirelessly during these FSK and ASK transmissions.

It is desirable for power transmitting device 12, power transmitting andreceiving device 18, and power receiving device 24 to be able tocommunicate information such as received power, battery states ofcharge, and so forth, to control wireless power transfer. However, theabove-described technology need not involve the transmission ofpersonally identifiable information in order to function. Out of anabundance of caution, it is noted that to the extent that anyimplementation of this charging technology involves the use ofpersonally identifiable information, implementers should follow privacypolicies and practices that are generally recognized as meeting orexceeding industry or governmental requirements for maintaining theprivacy of users. In particular, personally identifiable informationdata should be managed and handled so as to minimize risks ofunintentional or unauthorized access or use, and the nature ofauthorized use should be clearly indicated to users.

Control circuitry 16 has external object measurement circuitry 41 thatmay be used to detect external objects on the charging surface of thehousing of device 12 (e.g., on the top of a charging mat or, if desired,to detect objects adjacent to the coupling surface of a charging puck).The housing of device 12 may have polymer walls, walls of otherdielectric, and/or other housing wall structures that enclose coil(s) 36and other circuitry of device 12. The charging surface may be formed bya planer outer surface of the upper housing wall of device 12 or mayhave other shapes (e.g., concave or convex shapes, etc.). Inarrangements in which device 12 forms a charging puck, the charging puckmay have a surface shape that mates with the shape of device 24. A puckor other device 12 may, if desired, have magnets that removably attachdevice 12 to device 24 (e.g., so that coil 48 aligns with coil 36 duringwireless charging).

Circuitry 41 can detect foreign objects such as coils, paper clips, andother metallic objects and can detect the presence of wireless powerreceiving devices 24 (e.g., circuitry 41 can detect the presence of oneor more coils 48 and/or magnetic core material associated with coils48). During object detection and characterization operations, externalobject (foreign object) measurement circuitry 41 can be used to makemeasurements on coil(s) 36 such as Q-factor measurements, resonantfrequency measurements, and/or inductance measurements that can indicatewhether coil 48 is present and/or whether foreign objects such as coinsor paperclips are present. Measurement circuitry can also be used tomake sensor measurements using a capacitive sensor, can be used to maketemperature measurements, and/or can otherwise be used in gatheringinformation indicative of whether a foreign object or other externalobject (e.g., device 18 or 24) is present on device 12.

In some configurations, the control circuitry of device 12 (e.g.,circuitry 41 and/or other control circuitry 16) can implement a powercounting foreign object detection scheme. With this approach, device 12receives information from device 24 (e.g., via in-band communications)indicating the amount of power that device 24 is wirelessly receiving(e.g., 4.5 W). Device 12 knows how much power (e.g., 5.0 W) is beingtransmitted (e.g., because device 12 knows the magnitude of the signalbeing used to drive coil 36 from inverter 61). By comparing thetransmitted power (e.g., 5.0 W) to the received power (e.g., 4.5 W),device 12 can determine whether wireless power is being dissipated dueto eddy currents flowing in a foreign object. If the dissipated power(e.g., 0.5 W in this example) is more than a predetermined thresholdamount or if the efficiency of the wireless power transfer process islower than expected, device 12 can conclude that a foreign object ispresent. Power counting techniques such as these may be used inconjunction with capacitive sensing foreign object detection techniquesand/or other external object measurement operations performed usingcircuitry 41.

In some embodiments, measurement circuitry 41 of control circuitry 16contains signal generator circuitry (e.g., oscillator circuitry forgenerating AC probe signals at one or more probe frequencies, a pulsegenerator that can create impulses so that impulse responses can bemeasured) and/or uses the transmission of wireless power signals fromdevice 12 to energize the coils in system 8. Circuitry 41 may alsoinclude circuits (e.g., analog-to-digital converter circuits, filters,analog combiners, digital processing circuitry, etc.) to measure theresponse of system 8.

Power transmitting and receiving device 18 may be a wireless chargingmat or puck that is coupled to a power adapter or other equipment by acable, may be equipment that has been incorporated into furniture, avehicle, or other system, may be a removable battery case, may be aportable electronic device such as a wrist watch, a cellular telephone,a laptop computer, a tablet computer, an accessory such as an earbud, orother electronic equipment. Power transmitting and receiving device 18is capable of both transmitting and receiving wireless power. Powertransmitting and receiving device 18 therefore may include powertransmitting components, similar to power transmitting device 12. Powertransmitting and receiving device 18 may also include power receivingcomponents, similar to power receiving device 24.

Power transmitting and receiving device 18 may have analternating-current (AC) to direct-current (DC) power converter such asAC-DC power converter 96 for converting AC power from a wall outlet orother power source into DC power. DC power may be used to power controlcircuitry 78. Control circuitry 78 includes wireless transceivercircuitry 80 for in-band communications (using coils 90) and out-of-bandcommunications (using an antenna). Control circuitry 78 may alsooptionally include measurement circuitry 82 (e.g., measurement circuitryof the type described in connection with measurement circuitry 41).

Wireless power circuitry 84 in device 18 may include both an inverter 86and a rectifier 88. Inverter circuitry 86 (e.g., formed fromtransistors) may be turned on and off based on control signals providedby control circuitry 78 to create AC current signals through one or morecoils such as coil(s) 90. These coil drive signals cause coil(s) 90 totransmit wireless power. Coils 90 may be arranged in a planar coil arrayor may be arranged to form a cluster of coils. In some arrangements,device 18 may have only a single coil. In other arrangements, device 18may have multiple coils (e.g., two or more coils, 5-10 coils, at least10 coils, 10-30 coils, fewer than 35 coils, fewer than 25 coils, orother suitable number of coils).

As the AC currents pass through one or more coils 90,alternating-current electromagnetic (e.g., magnetic) fields (wirelesspower signals 44) are produced that are received by one or morecorresponding receiver coils such as coil(s) 48 in power receivingdevice 24. In other words, one or more of coils 90 may be inductivelycoupled to one or more of coils 48.

Power transmitting and receiving device 18 may also receive wirelesspower (e.g., from power transmitting device 12). Coil(s) 90 may receivealternating-current electromagnetic fields from transmitting coils 36,resulting in corresponding alternating-current currents in coil(s) 90.Rectifier circuitry such as rectifier circuitry 88, which containsrectifying components such as synchronous rectificationmetal-oxide-semiconductor transistors arranged in a bridge network,converts received AC signals (received alternating-current signalsassociated with electromagnetic signals 44) from one or more coils 90into DC voltage signals for powering device 18. The DC voltage producedby rectifier circuitry 88 can be used in charging a battery such asbattery 94 and can be used in powering other components in device 18.

The depiction of alternating-electromagnetic fields between each type ofdevice in FIG. 1 is merely illustrative (to show the type of inductivecoupling that is possible). In practice, alternating-electromagneticfields will only be conveyed between select devices within the system.For example, transmitting device 12 may transmit power to device 24 anddevice 18 (while device 18 does not separately transmit power to device18). In another example, transmitting device 12 transmits power todevice 18, which transmits power to 24 (without direct exchange of powerfrom device 12 to device 24).

In some applications, power transmitting and receiving device 18 onlytransmits wireless power (e.g., using inverter 86 and coil(s) 90). Insome applications, power transmitting and receiving device 18 onlyreceives wireless power (e.g., using rectifier 88 and coil(s) 90). Insome applications, power transmitting and receiving devicesimultaneously receives and transmits wireless power. Whensimultaneously receiving and transmitting wireless power, device 18 mayoptionally perform both the power transmitting and power receivingoperations associated with inverter 86 and rectifier 88 (e.g., device 18uses the rectifier to charge the battery and operate the device andindependently uses the inverter to transmit a desired amount of power).Alternatively, device 18 may relay received wireless power signalswithout rectifying the power. Device 18 may include only one coil thatis used for both wireless power transmission and wireless powerreception. Alternatively, device 18 may have at least one dedicatedwireless power transmitting coil and at least one dedicated wirelesspower receiving coil. Device 18 may have multiple coils that are allused for both wireless power transmission and wireless power reception.Different coils in device 18 may optionally be shorted together indifferent modes of operation.

FIG. 2 is a circuit diagram of illustrative wireless charging circuitryfor system 8. Wireless charging circuitry of a power transmitting device12 and a power receiving device 24 is shown. However, it should beunderstood that device 18 may have the corresponding components for bothpower transmission and power reception and may be used in place ofeither device 12 and/or device 24 if desired. As shown in FIG. 2 ,circuitry 52 may include inverter circuitry such as one or moreinverters 61 or other drive circuitry that produces wireless powersignals that are transmitted through an output circuit that includes oneor more coils 36 and capacitors such as capacitor 71. In someembodiments, device 12 may include multiple individually controlledinverters 61, each of which supplies drive signals to a respective coil36. In other embodiments, an inverter 61 is shared between multiplecoils 36 using switching circuitry.

During operation, control signals for inverter(s) 61 are provided bycontrol circuitry 16 at control input 74. A single inverter 61 andsingle coil 36 is shown in the example of FIG. 2 , but multipleinverters 61 and multiple coils 36 may be used, if desired. In amultiple coil configuration, switching circuitry (e.g., multiplexercircuitry) can be used to couple a single inverter 61 to multiple coils36 and/or each coil 36 may be coupled to a respective inverter 61.During wireless power transmission operations, transistors in one ormore selected inverters 61 are driven by AC control signals from controlcircuitry 16. The relative phase between the inverters can be adjusteddynamically. For example, a pair of inverters 61 may produce outputsignals in phase or out of phase (e.g., 180 degrees out of phase).

The application of drive signals using inverter(s) 61 (e.g., transistorsor other switches in circuitry 52) causes the output circuits formedfrom selected coils 36 and capacitors 71 to produce alternating-currentelectromagnetic fields (signals 44) that are received by wireless powerreceiving circuitry 54 using a wireless power receiving circuit formedfrom one or more coils 48 and one or more capacitors 72 in device 24.

If desired, the relative phase between driven coils 36 (e.g., the phaseof one of coils 36 that is being driven relative to another adjacent oneof coils 36 that is being driven) may be adjusted by control circuitry16 to help enhance wireless power transfer between device 12 and device24. Rectifier circuitry 50 is coupled to one or more coils 48 (e.g., apair of coils) and converts received power from AC to DC and supplies acorresponding direct current output voltage Vrect across rectifieroutput terminals 76 for powering load circuitry in device 24 (e.g., forcharging battery 58, for powering a display and/or other input-outputdevices 56, and/or for powering other components). A single coil 48 ormultiple coils 48 may be included in device 24. In an illustrativeconfiguration, device 24 may be a wristwatch or other portable devicewith at least two coils 48. These two (or more) coils 48 may be usedtogether when receiving wireless power. Other configurations may beused, if desired.

As previously mentioned, in-band transmissions using coils 36 and 48 maybe used to convey (e.g., transmit and receive) information betweendevices 12 and 24. With one illustrative configuration, frequency-shiftkeying (FSK) is used to transmit in-band data from device 12 to device24 and amplitude-shift keying (ASK) is used to transmit in-band datafrom device 24 to device 12. In other words, a device transmittingwireless power may use FSK to transmit in-band data to a devicereceiving wireless power (regardless of whether either device is adedicated power transmitting/receiving device 12/24 or a power receivingand transmitting device 18). A device receiving wireless power may useASK to transmit in-band data to a device transmitting wireless power(regardless of whether either device is a dedicated powertransmitting/receiving device 12/24 or a power receiving andtransmitting device 18).

Power may be conveyed wirelessly from device 12 to device 24 duringthese FSK and ASK transmissions. While power transmitting circuitry 52is driving AC signals into one or more of coils 36 to produce signals 44at the power transmission frequency, wireless transceiver circuitry 40may use FSK modulation to modulate the power transmission frequency ofthe driving AC signals and thereby modulate the frequency of signals 44.In device 24, coil 48 is used to receive signals 44. Power receivingcircuitry 54 uses the received signals on coil 48 and rectifier 50 toproduce DC power. At the same time, wireless transceiver circuitry 46monitors the frequency of the AC signal passing through coil(s) 48 anduses FSK demodulation to extract the transmitted in-band data fromsignals 44. This approach allows FSK data (e.g., FSK data packets) to betransmitted in-band from device 12 to device 24 with coils 36 and 48while power is simultaneously being wirelessly conveyed from device 12to device 24 using coils 36 and 48.

In-band communications between device 24 and device 12 may use ASKmodulation and demodulation techniques. Wireless transceiver circuitry46 transmits in-band data to device 12 by using a switch (e.g., one ormore transistors in transceiver 46 that are coupled coil 48) to modulatethe impedance of power receiving circuitry 54 (e.g., coil 48). This, inturn, modulates the amplitude of signal 44 and the amplitude of the ACsignal passing through coil(s) 36. Wireless transceiver circuitry 40monitors the amplitude of the AC signal passing through coil(s) 36 and,using ASK demodulation, extracts the transmitted in-band data from thesesignals that was transmitted by wireless transceiver circuitry 46. Theuse of ASK communications allows ASK data bits (e.g., ASK data packets)to be transmitted in-band from device 24 to device 12 with coils 48 and36 while power is simultaneously being wirelessly conveyed from device12 to device 24 using coils 36 and 48.

The example of FSK modulation being used to convey in-band data frompower transmitting device 12 to power receiving device 24 and ASKmodulation being used to convey in-band data from power receiving device24 to power transmitting device 12 is merely illustrative. In general,any desired communication techniques may be used to convey informationfrom power transmitting device 12 to power receiving device 24 and frompower receiving device 24 to power transmitting device 12. In general,wireless power may simultaneously be conveyed between devices duringin-band communications (using ASK or FSK).

The power transmission frequency used for transmission of wireless powermay be, for example, a predetermined frequency of about 125 kHz, atleast 80 kHz, at least 100 kHz, between 100 kHz and 205 kHz, less than500 kHz, less than 300 kHz, or other suitable wireless power frequency.In some configurations, the power transmission frequency may benegotiated in communications between devices 12 and 24. In otherconfigurations, the power transmission frequency may be fixed.

It has been described that power may be simultaneously conveyed betweendevices while using in-band communication for data transmission betweenthe devices. In other words, in some examples in-band communications mayrely on modulation of the power transmission signal (e.g., modulatingthe power transmission frequency or modulating amplitude of a signal atthe power transmission frequency). However, other communicationtechniques may be used that do not rely on modulation of the powertransmission signals. For example, signals (sometimes referred to asin-band signals) may be conveyed between coils in the system at afrequency that is different than the power transmission frequency.Signals (at the same frequency or a different frequency than the powertransmission frequency) that are conveyed using the coils (e.g., coils36, 48, and 90) may be considered in-band signals.

Moreover, it should be noted that in-band communication may occurbetween devices before the devices agree upon a power transfer rate,power transmission frequency, etc. After initial detection and inductivecoupling, devices may go through a handshake process to determinecompatibility, negotiate power transfer frequency, negotiate powertransfer rate, etc. During this process, in-band communication mayinvolve FSK and/or ASK modulation of signals at the power transmissionfrequency. Therefore, wireless power is transmitted during this process.This is advantageous as it allows the devices to complete the handshakeprocess even if the power receiving device has little or no remainingbattery power. This transmission of wireless power during in-bandcommunications may occur during the handshake process even if,ultimately, the negotiations between the devices result in no sustainedtransmission of wireless power (e.g., even if the devices do not enter adedicated power transfer phase).

The aforementioned FSK and ASK modulation and demodulation techniquesmay be used to transmit data packets between any two devices withinsystem 8. Each data packet may include numerous data bits (sometimesreferred to as bits). The data bits may be grouped into bytes, with eachbyte including any desired number of bits (e.g., 8 bits).

At least one coil in power transmitting and receiving device 18 may beused for transmitting or receiving wireless power (depending on theconditions within the wireless charging system). However, the coil doesnot transmit and receive wireless power at the same time. Therefore,control circuitry within the device may be used to control whether thecoil is used for transmitting or receiving wireless power at any giventime.

A protocol may be used to determine whether a given coil in powertransmitting and receiving device 18 is used for transmitting orreceiving wireless power. The protocol may take into account manyfactors such as the type of devices in the wireless charging system, thebattery charge levels of devices in the wireless charging systems,and/or whether the devices in the wireless charging system are coupledto additional power sources (e.g., tethered or untethered). The protocolmay place a coil in power transmitting and receiving device 18 in theoptimal mode for the given system conditions.

When a power transmitting and receiving device 18 is added to thewireless charging system, it may be desirable for the device to enter anappropriate mode and commence power transfer as quickly as possible. Auser notification may also be output by one or more devices in thecharging system to notify a user that the power transmitting andreceiving device 18 has been added to the charging system. The usernotification may indicate whether the power transmitting and receivingdevice 18 is being used to transmit and/or receive charge. Ideally,there is minimal latency between the device being added to the systemand the user notification being output to the user. One way to minimizelatency in most use cases is to assign each device a default mode. Thedefault mode may correspond to the most likely mode for a coil that caneither transmit or receive wireless charge.

Consider, for example, a cellular telephone with a wireless power coilthat is configured to either transmit or receive charge. In most usecases, the cellular telephone may be used to receive wireless power(e.g., when the cellular telephone is placed on a charging mat).However, in some use cases, the cellular telephone may be used totransmit wireless power (e.g., to an additional electronic device).Because the most common use case is that the cellular telephone receiveswireless power, the wireless power coil may have a default mode ofreceiving wireless power.

As another example, consider the example of a battery case with awireless power coil that is configured to either transmit or receivecharge. In most use cases, the battery case may be used to transmitwireless power (e.g., to a cellular telephone held by the case).However, in some use cases, the battery case may be used to receivewireless power (e.g., from a charging mat). Because the most common usecase is that the battery case transmits wireless power, the wirelesspower coil may have a default mode of transmitting wireless power.

FIG. 3 is a state diagram showing how a power transmitting and receivingdevice may switch between a power transmitting mode and a powerreceiving mode. For simplicity, an example where the device includes asingle coil will first be considered. In this example, the single coilmay be used for either transmitting power in mode 102 or receiving powerin mode 104. In the power transmitting mode 102, inverter 86 in wirelesspower circuitry 84 (see FIG. 1 ) may be used to transmit wireless powersignals using the coil. The coil, wireless power circuitry, and/oroverall device may be referred to as being in the power transmittingmode 102. In the power receiving mode 104, rectifier 88 in wirelesspower circuitry 84 (see FIG. 1 ) may be used to rectify wireless powersignals received using the coil. The coil, wireless power circuitry,and/or overall device may be referred to as being in the power receivingmode 104.

In the power transmitting mode 102, rectifier circuitry (of rectifier88) coupled to the coil may be disabled while the inverter circuitry (ofinverter 86) is enabled. Similarly, in the power receiving mode 104,inverter circuitry (of inverter 86) coupled to the coil may be disabledwhile rectifier circuitry (of rectifier 88) is enabled.

In the power transmitting mode 102, wireless transceiver circuitry 80may be configured to use frequency-shift keying (e.g., FSK modulation)to transmit information to the corresponding power receiving deviceusing the coil while simultaneously transmitting wireless power to thepower receiving device using the coil. In the power transmitting mode102, wireless transceiver circuitry 80 may be configured to useamplitude-shift keying (e.g., ASK demodulation) to receive informationfrom the corresponding power receiving device using the coil whilesimultaneously transmitting wireless power to the power receiving deviceusing the coil. In the power receiving mode 104, wireless transceivercircuitry 80 may be configured to use amplitude-shift keying (e.g., ASKmodulation) to transmit information to the corresponding powertransmitting device using the coil while simultaneously receivingwireless power from the power transmitting device using the coil. In thepower receiving mode 104, wireless transceiver circuitry 80 may beconfigured to use frequency-shift keying (e.g., FSK demodulation) toreceive information from the corresponding power transmitting deviceusing the coil while simultaneously receiving wireless power from thepower transmitting device using the coil. This example is merelyillustrative. In general, any desired communication scheme may be used.

The example of device 18 having a single coil that is either in a powertransmitting mode or power receiving mode is merely illustrative. Ingeneral, device 18 may have any desired number of coils. Some of thecoils may only transmit wireless power. Some of the coils may onlyreceive wireless power. Some of the coils may either transmit or receivewireless power. Of the coils that transmit or receive wireless power,the control circuitry may control the operating mode of the coilscollectively or individually. Herein, for simplicity, an example isdescribed of a power transmitting and receiving device 18 with a singlecoil that either transmits or receives wireless power.

As previously mentioned, a device may have an associated default modefor each coil that is capable of operating in either a transmitting orreceiving mode. When two power transmitting and receiving devices areplaced adjacent to one another (e.g., aligning coils in the two devicesfor wireless power transfer), the devices may attempt to establish apower transfer link. In one illustrative scheme, the devices could berandomly assigned a role (e.g., power transmitter or power receiver).However, instead of assigning initial roles randomly, using the defaultroles as discussed above may minimize the time for establishing a powertransfer link and notifying the user of the link between the devices.Accordingly, during the identification, configuration, and/ornegotiation phases between the two devices, each device may assume itsdefault role. If the real-time conditions of the wireless chargingsystem dictate that the devices be in their non-default roles, one ofthe devices may request a role swap (sometimes referred to as modechange). For example, a default power receiver may switch to a powertransmitting mode and/or a default power transmitter may switch to apower receiving mode. The role swap may occur either before or during apower transfer phase.

FIGS. 4A and 4B are timing diagrams showing how devices may start intheir default roles and ultimately switch roles before starting a powertransfer phase. In the example of FIGS. 4A and 4B, a first device(device 1) is placed adjacent to a second device (2). Both device 1 anddevice 2 may be power transmitting and receiving devices and thereforecapable of operating in both a power transmitting mode and powerreceiving mode. Device 1 may be a cellular telephone that has a defaultmode of a power receiving mode. Device 2 may be a battery case that hasa default mode of a power transmitting mode. Therefore, device 1initially operates as a power receiving device and device 2 initiallyoperates as a power transmitting device.

As shown in FIG. 4A, device 1 may detect the presence of an additionaldevice at t₁. Device 1 may detect the additional device using a changein a sensor within device 1. For example, input-output components 92 (asin FIG. 1 ) of device 1 may include a sensor that is sensitive toelectromagnetism such as a near-field communications (NFC) coil or Halleffect sensor (a sensor that measures the magnitude of a magneticfield). As another example, the input-output components 92 may includean accelerometer that is configured to detect when device 1 bumps intoan additional device (e.g., device 2). Device 1 may also detect device 2using the wireless power coil itself (e.g., coil 90 that is also used totransmit or receive wireless power). In general, input from any subset(e.g., one or more) of the aforementioned components may be used todetect the presence of device 2.

Once device 2 is detected at t₁, device 1 may optionally initiate an NFCscan at t₂. The NFC scan may be used to identify the device type ofdevice 2 and/or obtain other information from device 2.

Device 2 is operating as a transmitting device based on its defaultmode. Device 2 may detect the presence of device 1 similarly to howdevice 1 detects the presence of device 2 (e.g., using the coil, asensor that is sensitive to electromagnetism, using an accelerometer,etc.). Ultimately, device 2 may enter a ping phase (to determine if theadditional device detected is a compatible device for wireless chargingoperations). During the ping phase, device 2 attempts to establishcommunication with device 1. As shown, at t₃, device 2 may execute adigital ping during which a power signal is applied to the coil indevice 2. The term digital ping may refer to a longer ping that powersup the receiver device (as opposed to an analog ping that may be used toinitially detect the presence of the receiver device). The term ping maysometimes be used in place of digital ping for simplicity. If acompatible power receiver is indeed present (as in FIG. 4A), thereceiver may detect the power field from the digital ping and provide aresponse (e.g., via ASK in-band communication) and the devices may enteran identification and configuration phase. If no compatible powerreceiver were present, the power transmitter (device 2) may revert to aselection phase (in which the transmitter monitors for adjacent objectsthat may potentially be power receivers).

In FIG. 4A, device 1 receives the digital ping at t₃ and the devicesenter an identification and configuration phase. During theidentification and configuration phase, devices 1 and 2 may exchangeinformation such as the amount of power wanted by the receiver, theamount of power available from the transmitter, etc. A negotiation phasemay also occur during which a power transfer amount is negotiated andagreed upon by both devices. Once the devices agree upon a powertransfer level, the devices will enter a power transfer phase duringwhich sustained wireless power transfer occurs at the agreed upon powertransfer level. The communications before the power transfer phase maycollectively be referred to as a configuration phase, identification andconfiguration phase, identification phase, negotiation phase,handshaking phase, etc. Alternatively or in addition, the communicationsbefore the power transfer phase may be grouped into different phases(e.g., a configuration phase, an identification phase, and a negotiationphase).

As shown in FIG. 4A, at t 4 device 1 may send aconfiguration/capabilities packet 106 (sometimes referred to as simplyconfiguration packet 106 or capabilities packet 106) to device 2.Because device 1 is operating in a receiving mode, the packet may besent from device 1 using ASK modulation (e.g., by modulating a powersignal received from device 2 as part of the digital ping) while device1 simultaneously receives wireless power from device 2. Theconfiguration/capabilities packet may include at least one bit thatindicates whether or not the receiver is capable of swapping modes(e.g., switching from a receiving mode to a transmitting mode). As oneexample, a dedicated power receiving device (e.g., device 24 in FIG. 1 )may set this bit equal to ‘0’ and a power transmitting and receivingdevice (e.g., device 18 in FIG. 1 ) may set this bit equal to ‘1’.

The bit indicative of the receiving device's swap capabilities may beincorporated into a configuration packet that includes other informationsuch as power class, maximum power value, window size, window offset, a‘Prop’ bit, a ‘Neg’ bit, a polarity bit that provides informationregarding FSK polarity, depth bits used to select FSK modulation depth,and/or a count identifying how many optional configuration packets willbe transmitted. Alternatively, the bit indicative of the receivingdevice's swap capabilities may be incorporated into a dedicated packetthat includes other information relevant to the potential role swappingof the device (e.g., state of charge information, whether or not thedevice is tethered to wired power, etc.).

At t₅ device 2 may send a configuration/capabilities packet 108(sometimes referred to as simply configuration packet 108 orcapabilities packet 108) to device 1. Because device 2 is operating in atransmitting mode, the packet may be sent from device 2 using FSKmodulation while simultaneously transmitting wireless power to device 1(e.g., by modulating the power signal used for the digital ping). Theconfiguration/capabilities packet may include at least one bit thatindicates whether or not the transmitter is capable of swapping modes(e.g., switching from a transmitting mode to a receiving mode). As oneexample, a dedicated power transmitting device (e.g., device 12 in FIG.1 ) may set this bit equal to ‘0’ and a power transmitting and receivingdevice (e.g., device 18 in FIG. 1 ) may set this bit equal to ‘1’.

The bit indicative of the transmitting device's swap capabilities may beincorporated into a capabilities packet that includes other informationsuch as negotiable load power, potential load power, and/or buffer size.Alternatively, the bit indicative of the transmitting device's swapcapabilities may be incorporated into a dedicated packet that includesinformation relevant to the potential role swapping of the device (e.g.,state of charge information, whether or not the device is tethered towired power, etc.).

Once the devices have exchanged the swap capability information andother pertinent information, control circuitry within one or bothdevices may determine whether or not to initiate a role swap. Based onthe real-time conditions, it may sometimes be desirable for device 1 toswap from its default receiving mode to a transmitting mode and transmitwireless power to device 2 (which would swap from its defaulttransmitting mode to a receiving mode). Either device 1 or device 2 mayinitiate a swap request based on the real time conditions. In oneexample, control circuitry in the receiving device use a power protocolto determine whether a role swap is appropriate. The receiving devicemay, based on the information regarding the transmitter capabilities andother information, in some cases determine that a role swap isappropriate.

After determining that a role swap is appropriate, device 1 may send aswap request packet 110 at t₆. The swap request packet may include areason for the swap request. As one example, device 1 may be tethered toa wired power source. The power protocol may dictate that device 1serves as a transmitter in this condition. Therefore, the swap requestpacket 110 may include the presence of the tether as the reason for theswap.

Device 2 may accept the power swap request and switch to a receiver modeat t₇. Device 2 may optionally send an acknowledgement back to device 1indicating that the swap request is accepted. In some instances, device2 may choose to deny the swap request (e.g., if device 2 is alsotethered and therefore does not need to receive wireless power). Whileswitching to the receiver mode, device 2 may end the digital ping (whichwas used for in-band communication between t₃ and t₇).

As show in FIG. 4B (which is simply a continuation of the timing diagramof FIG. 4A), device 1 may optionally start an NFC scan at t₈. The NFCscan may be used to identify the device type of device 2 and/or obtainother information from device 2.

At t₉, device 1 may perform a user interface (UI) update. The userinterface update may include a user notification that is output to theuser (e.g., using a display, status indicator light, speakers, hapticoutput device, or another desired input-output component). The usernotification may indicate that the power transmitting and receivingdevice is operating in a transmitting mode. The user notification mayalso include information such as the state of charge of a battery indevice 2 and/or the state of charge of the battery of device 1.

At t₁₀, now in the power transmitting mode, device 1 may enter a digitalping phase during which a power signal is applied to the coil in device1. Device 2 (now in the power receiving mode) may detect the power fieldfrom the digital ping and provide a response (e.g., via ASK in-bandcommunication). The devices may enter an identification andconfiguration phase, negotiate a power transfer level, and ultimatelyenter a power transfer phase with sustained wireless power transfer atthe negotiated level.

It should be noted that the user interface update at t₉ may be designedto optimize user experience. In other words, the user interface updateneed not reflect the actual modes and timing of the operation of device1. In practice, device 1 is operating in a power receiving mode and isreceiving power signals (from the digital ping) between t₃ and t₆.However, since this initial mode may be later changed before entering apower transfer phase (as is the case in FIGS. 4A and 4B), the usernotification may not yet be output.

Once device 1 switches modes from a receiving mode to a transmittingmode, the user notification may be output (even before device 1 enters apower transfer phase with device 2). Once device 1 sends the swaprequest at t₆, it is known that device 1 will ultimately be operating ina power transmitting mode. Similarly, all information regarding device 2(e.g., state of charge information, device type information) is known byt₆ . Therefore, at t₆ device 1 may begin loading the user interfaceupdate and output the user notification as soon as possible (to minimizelatency between the devices being placed together and the notificationbeing output). In this example it takes the time between t₆ and t₉ forthe user notification to be prepared and loaded. Once ready, the usernotification is output at t₉ . Again, the user notification may indicatethat device 1 is actively transferring power to device 2 even though thedevices have not negotiated and entered a power transfer phase yet.

To summarize, the user notification may be designed to reflect theexpected final outcome of the wireless power exchange between the twodevices. The user notification may be output based on the expected finaloutcome before the final outcome is actually achieved, and the usernotification may not reflect intermediate states that occur before thefinal outcome. This scheme optimizes the experience for the user.

FIG. 5 is a timing diagram showing another example of a device startingin a default role and ultimately switching roles before starting a powertransfer phase. In the example of FIG. 5 , a first device (device 1) isplaced adjacent to a second device (2). Device 1 may be a powertransmitting and receiving device and is therefore capable of operatingin both a transmitting mode and receiving mode. Device 2 may be adedicated power receiving device (e.g., an accessory that only receiveswireless power) or a power transmitting and receiving device with a deadbattery (that therefore can only receive power at this time). Device 1may be a cellular telephone that has a default mode of a power receivingmode. Device 2 may be an accessory that is a dedicated wireless powerreceiver. Therefore, device 1 initially operates as a power receivingdevice and device 2 also initially operates as a power receiving device.

As shown in FIG. 5 , device 1 may detect the presence of an additionaldevice at t₁. Device 1 may detect the additional device using a changein a sensor within device 1 (e.g., a sensor that is sensitive toelectromagnetism such as an NFC coil or Hall effect sensor, anaccelerometer, etc.) or a change detected by the wireless power coil.Once device 2 is detected at t₁, device 1 may optionally initiate an NFCscan at t₂. The NFC scan may be used to (attempt to) identify the devicetype of device 2 and/or obtain other information from device 2. However,in this case device 2 may not have NFC communication functionality(either because device 2 is a dedicated receiver without NFCcommunication capabilities or device 2 has a dead battery and cannotcommunicate). Therefore, the NFC scan may conclude at t₃ withoutcommunicating with device 2.

The lack of communication during the NFC scan is indicative of the stateof device 2. This information, in combination with the detected changeat t₁ indicating the presence of a device, may be used by device 1 todetermine that device 2 is only capable of receiving wireless power atpresent conditions. At t₄, after a predetermined length of time haspassed from initial detection at t₁ without receiving a digital pingfrom the detected device, device 1 may ‘timeout’ and switch modes fromthe default power receiving mode to a power transmitting mode. Thetimeout may be sufficiently long to guarantee that device 1 would havereceived a digital ping (if device 2 was indeed operating in atransmitting mode). Once the timeout period expires without receivingthe digital ping, device 1 switches from its default role into a powertransmitting mode. The timeout period may be any desired length of time(e.g., more than 300 milliseconds, more than 400 milliseconds, more than500 milliseconds, more than 1 second, less than 1 second, between 300milliseconds and 700 milliseconds, between 450 milliseconds and 550milliseconds, etc.).

After switching to the power transmitter mode, device 1 may enter adigital ping phase at is during which a power signal is applied to thecoil in device 1. Device 2 (which is in a receiving mode) may detect thepower field from the digital ping and provide a response (e.g., via ASKin-band communication).

As shown in FIG. 5 , device 2 receives the digital ping at is and thedevices enter an identification and configuration phase. During theidentification and configuration phase, devices 1 and 2 may exchangeinformation such as the amount of power wanted by the receiver, theamount of power available from the transmitter, etc. A negotiation phasemay also occur during which a power transfer amount is negotiated andagreed upon by both devices.

As shown in FIG. 5 , at t₆ device 2 may send a receiverconfiguration/capabilities packet 106 to device 1. Because device 2 isoperating in a receiving mode, the packet may be sent from device 2using ASK modulation (e.g., by modulating a power signal received fromdevice 1 as part of the digital ping) while simultaneously receivingwireless power from device 1. The configuration/capabilities packet mayinclude at least one bit that indicates whether or not the receiver iscapable of swapping modes (e.g., switching from a power receiving modeto a power transmitting mode).

At t₇ device 1 may send a transmitter configuration/capabilities packet108 to device 2. Because device 1 is operating in a transmitting mode,the packet may be sent from device 1 using FSK modulation whilesimultaneously transmitting wireless power to device 2 (e.g., bymodulating the power signal used for the digital ping). Theconfiguration/capabilities packet may include at least one bit thatindicates whether or not the transmitter is capable of swapping modes(e.g., switching from a power transmitting mode to a power receivingmode).

When device 1 receives the capabilities packet 106 at t₆, device 1 hassufficient information to prepare and load a user notification to updatethe charging state of device 1. Similar to as discussed in connectionwith FIGS. 4A and 4B, the user notification may be prepared and loadedbefore the devices actually enter the power transfer phase. At t₆ inFIG. 5 , device 1 knows that it will be transferring power to device 2and knows any additional necessary information from device 2 (e.g.,state of charge information, device type, etc.). Therefore, the usernotification (sometimes referred to as a chime) may be initiated at t₆.

The user interface update may be performed at t₈ (e.g., as soon aspossible once loaded). It should be noted that user interface updates(e.g., as described in connection with device 1 in FIGS. 4 and 5 ) mayalso occur in device 2. The device 2 user interface updates may occureither synchronously or asynchronously with the device 1 user interfaceupdates. In some cases, devices 1 and 2 may synchronously output anaudio, visual, and/or haptic indicator.

The user notification (e.g., output) from devices 1 and 2 may includeone or more of audio feedback, visual feedback, haptic feedback, and anyother desired type of feedback. For example, the devices may useinput-output devices such as a display (e.g., to display an animation orother visual feedback), a status indicator light (e.g., to providevisual feedback) a speaker (e.g., to provide an audio indicator), or avibrator (e.g., to provide haptic feedback) in the user notification(sometimes referred to as an indicator or output). Different devices mayprovide different feedback. For example, a cellular telephone andwristwatch may use the display to display an animation and use avibrator to provide haptic feedback. A battery case for earbuds may usea status indicator light to provide visual feedback.

The example of an NFC scan in FIGS. 4 and 5 is merely illustrative. Ingeneral, any desired communication (e.g., Bluetooth communications) maybe used in place of the NFC scan.

As previously discussed, the configuration/capabilities packets 106 and108 may optionally be dedicated packets for transmitting informationrelevant to the capabilities/configuration/status of the device. FIG. 6is a diagram of an illustrative packet that may be used for eitherpacket 106 or packet 108. As shown, the packet includes a first byte(B₀) with a bit (b₇) that indicates whether or not the device (e.g., thedevice sending the packet) is capable of swapping roles (e.g., switchingfrom a power transmitting mode to a power receiving mode or vice versa).As one example, the swap bit may be a first value (1′) when the deviceis a power transmitting and receiving device and the swap bit may be asecond value (0′) when the device is a dedicated power transmittingdevice or a dedicated power receiving device.

The first bye also includes a bit (b₆) that indicates whether or not thedevice is tethered. As one example, the tethered bit may be a firstvalue (1′) when the device has a connection to an external power source(e.g., plugged into a wall outlet). The connection to external power maynormally be wired but in some cases may be wireless. The tethered bitmay be a second value (0′) when the device does not have a connection toan external power source (e.g., is not plugged into a wall outlet). Bitsb₀through b₅ are reserved.

The packet may also include a byte (B₁) with at least one bit (e.g., b₀through b₆ in FIG. 6) for conveying the state of charge (battery level)of a battery within the device. There may be a predetermined value thatindicates that the device does not have a battery (e.g., for powertransmitters without an internal battery). Otherwise, the battery levelrepresents the current state of charge of the device battery.

FIG. 7 is a diagram of an illustrative packet that may be used for aswap request (sent by either a power transmitter or power receiver). Asshown, packet 110 may include one byte with a plurality of bits (e.g.,bits b₀ through b₇) that are used to identify a reason for the swaprequest. Reasons for the swap request may include a power source change(e.g., the device is newly tethered or the device is newly untethered),a battery level increase, a battery level decrease, a user requestedchange, etc. The user requested change may occur when the user usesinput-output components within the device to manually swap the powermode of the device (e.g., from a power transmitting mode to a powerreceiving mode or vice versa).

A power role swap may occur either before a power transfer phase orduring a power transfer phase. The need for a power role swap may bedetermined according to a power protocol that identifies circumstancessufficient to warrant a role swap. There are many types of guidelinesthat may be used by the power protocol to make power roledeterminations. As one example, it may be preferred for tethered devices(e.g., devices coupled to an external power source such as a wired powersource) to operate in a power transmitting mode to charge other devices.If a power transmitting and receiving device that is a default powerreceiver is tethered, the power protocol may suggest swapping the powertransmitting and receiving device from the power receiving mode to thepower transmitting mode.

As another example, it may be preferred for devices with higher batterycharge level to be in a power transmitting mode and devices with lowerbattery levels to be in a power receiving mode. The battery chargelevels (e.g., states of charge) may be compared to both predeterminedthresholds and/or each other. For example, there may be a first state ofcharge threshold used to identify ‘high’ state of charge devices (e.g.,80%, 90%, 95%, more than 80%, more than 50%, between 60% and 90%, etc.).A device having a state of charge greater than the threshold may beconsidered a high state of charge device. Similarly, there may be asecond state of charge threshold used to identify ‘low’ state of chargedevices (e.g., 40%, 30%, 20%, 10%, 5%, less than 30%, less than 50%,between 1% and 30%, etc.). A device having a state of charge lower thanthe threshold may be considered a low state of charge device. Deviceshaving a high state of charge may be preferred to be power transmitterswhereas devices having a low state of charge may be preferred to bepower receivers.

The state of charge of two devices may also be compared to each other.The device having a higher state of charge may be preferred to be apower transmitter and the device having a lower state of charge may bepreferred to be a power receiver. In some cases, the state of chargedifference may need to be greater than a threshold magnitude to warranta role swap. For example, consider the example of a laptop computer thatis capable of both transmitting and receiving wireless power and acellular telephone that is capable of both transmitting and receivingwireless power. The laptop computer may be a default power transmitterwhereas the cellular telephone may be a default power receiver. If thelaptop computer's state of charge is 50% and the cellular telephone'sstate of charge is 55%, the devices may maintain their default roles andthe laptop may transfer wireless power to the cellular telephone. If thelaptop computer's state of charge is 10% and the cellular telephone'sstate of charge is 90%, the devices may switch from their default rolesand the cellular telephone may transfer wireless power to the laptopcomputer. In the 10%/90% example, the difference in state of charge maybe greater than a threshold (e.g., 10%, 20%, 30%, 40%, 50%, between 5%and 60%, less than 50%, etc.). The difference in state of charge may beused in combination with the status of one or more devices as high orlow state of charge devices to determine whether a role swap isappropriate.

FIGS. 8 and 9 are diagrams showing how a role swap request may be senteither before or during a power transfer phase. FIG. 8 shows an exampleof a role swap occurring before a power transfer phase. First, a roleswap request 111 may be sent from device 1 to device 2. The role swaprequest 111 may include a packet (e.g., packet 110 in FIG. 7 ) with areason for the swap request. After receiving the request, device 2 maysend a response 112 (acknowledgement) accepting the swap request.Accordingly, the devices swap power roles at power role swap 114. Oncethe power roles have swapped, the devices may proceed to the negotiationphase 116. An identification and configuration phase may also beincluded after the power role swap if desired. Finally, after thedevices have agreed upon a power transfer level, the devices may enterthe power transfer phase 118 (during which sustained power transmissionoccurs).

FIG. 9 shows an example of a role swap occurring during a power transferphase. As shown, the devices may be in a power transfer phase 122 (e.g.,sustained power transmission at an agreed upon power level). Then, whilewireless power is being transmitted, a role swap request 124 may be sentfrom device 1 to device 2. The role swap request 124 may include apacket (e.g., packet 110 in FIG. 7 ) with a reason for the swap request.After receiving the request, device 2 may send a response 126(acknowledgement) accepting the swap request. Accordingly, the devicesswap power roles at power role swap 128. After swapping power roles, thedevices may proceed through one or more of identification,configuration, and negotiation phases and ultimately commence a newpower transfer phase using the new roles.

In FIGS. 8 and 9 , device 1 may start either in a power transmittingmode or power receiving mode. Similarly, device 2 may start either in apower transmitting mode or power receiving mode.

As a first example of a situation where a role swap may occur, consideran example where a tethered cellular telephone is placed adjacent to anuntethered battery case. The cellular telephone may default to a powerreceiving mode and the battery case may default to a power transmittingmode. Inductive coupling (sometimes referred to as an inductive link)may be established with the devices in their default modes (e.g., usinga digital ping transmitted from the battery case to the cellulartelephone). Using the inductive coupling, the devices may exchangecapability information (e.g., state of charge information, tether statusinformation, device type information, swap capability information,etc.). Based on the exchanged information, control circuitry in one orboth devices may generate an instruction to swap roles based on a powerprotocol. In this case, it is preferred for the tethered cellulartelephone to be a power transmitter. Therefore, the cellular telephonesends a swap request to the battery case. The battery case accepts therequest and the devices swap roles. After swapping roles, the cellulartelephone transmits wireless power to the battery case.

While the cellular telephone transmits wireless power to the batterycase, the cellular telephone may switch from the tethered state to theuntethered state (e.g., the cellular telephone may be disconnected froma wired power source). This change in status of the cellular telephonemay be conveyed from the cellular telephone to the battery case (e.g.,using a capabilities packet 108). Based on the updated status of thecellular telephone, control circuitry in one or both devices maygenerate an instruction to swap roles based on a power protocol. Nowthat the cellular telephone is no longer tethered, it may be desired forthe cellular telephone to revert to its default role as a powerreceiver. Therefore, the devices may swap roles. After swapping roles,the battery case transmits wireless power to the cellular telephone.

As another example of a situation where a role swap may occur, consideran example where a first untethered cellular telephone is placedadjacent to a second untethered cellular telephone. The cellulartelephones may both default to a power receiving mode. In this case, thecellular telephone with the higher state of charge may swap to a powertransmitting mode and transmit wireless power to the cellular telephonewith the lower state of charge.

FIG. 10 is a flowchart showing illustrative method steps for operating apower transmitting and receiving device (e.g., device 18 in FIG. 1 )during coupling with another device. As shown, at step 132 the powertransmitting and receiving device may detect the presence of anadditional electronic device (e.g., using a wireless power coil 90 oranother component such as an accelerometer, Hall effect sensor, NFCcoil, etc.). In response to detecting the additional electronic device,the wireless power circuitry and wireless power coil in device 18 mayenter a configuration phase and may be placed in a default mode at step134. The default mode may be the mode device 18 (and specifically awireless power coil and corresponding wireless power circuitry in thedevice) reverts to every time device 18 is placed adjacent an externalelectronic device (e.g., each time device 18 newly enters theconfiguration phase with a newly detected device). In other words, eachtime an additional device is detected at step 132, the coil and wirelesspower circuitry are placed in the same default mode (e.g., powerreceiving mode 104 or power transmitting mode 102). It should be notedthat, if an untethered power transmitting and receiving device has abattery that is dead (e.g., no charge level remaining), the device isnecessarily in a receiving mode as there is no power with which todetect an additional device and enter a configuration phase in atransmitting mode.

After the wireless power circuitry is placed in the default mode, thedevice may attempt to establish inductive coupling with the additionalelectronic device (e.g., by transmitting or receiving a digital ping).If the inductive coupling is established at step 136, the method mayproceed to step 140. When the default mode is a power transmitting mode,the device may know the inductive coupling is established upon receivinga packet from the additional device (e.g., an ASK packet) in response tothe transmitted digital ping. When the default mode is a power receivingmode, the device may know the inductive coupling is established uponreceiving a digital ping from the additional device.

If the inductive coupling is not established within a predeterminedperiod of time (e.g., the timeout threshold discussed in connection withFIG. 5 ), the method may proceed to step 138. At step 138, the devicemay switch the mode of the wireless power circuitry and coil from thedefault mode to an alternate mode. In other words, control circuitry inthe power transmitting and receiving device is configured to interpretthe timeout as an instruction representing a mode change. If the defaultmode is a power transmitting mode, the device may switch from the powertransmitting mode to a power receiving mode. If the default mode is apower receiving mode, the device may switch from the power receivingmode to a power transmitting mode. After switching from the default modeat step 138, the power transmitting and receiving device would aim toagain establish inductive coupling with the additional electronicdevice. Assuming the inductive coupling is established, the methodproceeds to step 140.

At step 140, in-band communication may be used for the powertransmitting and receiving device and additional electronic device toexchange information such as mode change capabilities (e.g., is thedevice capable of changing modes) and wireless charging information(e.g., state of charge information, tethering information, device type,etc.). Packets 106 and 108 shown and discussed in connection with FIGS.4-6 may be used to exchange some or all of this information. The devicesmay each transmit a packet that include at least one bit representativeof the role swap capabilities of that device.

After exchanging the information in step 140, the devices may switchmodes if appropriate at step 142. The optional mode switch may bedetermined based on a power protocol used by control circuitry in one orboth devices. Control circuitry in the power transmitting and receivingdevice may interpret output from the power protocol as an instructionrepresenting a mode change. The mode change may occur before the powertransfer phase commences. The device may switch from the default moderesponsive to the state of charge of one or both devices, responsive toone of the devices being coupled to a wired power source, etc. As aspecific example, a default wireless power receiver may switch to awireless power transmitting mode if the default wireless power receiveris coupled to a wired charging source such as main power.

Next, at step 144, the devices may enter a power transfer phase (e.g.,at a negotiated power transfer level). During the power transfer phase,the devices may switch modes if appropriate at step 146. This optionalmode switch may be determined based on a power protocol used by controlcircuitry in one or both devices. Control circuitry in the powertransmitting and receiving device may interpret output from the powerprotocol as an instruction representing a mode change. The device mayswitch from the default mode responsive to the state of charge of one ofthe devices dropping below a predetermined threshold, responsive to thepower receiving device being coupled to a wired power source, etc.

A battery-powered device may transmit its state of charge to a powerreceiving device using in-band communication. Both dedicated powertransmitting devices (e.g., device 12 in FIG. 1 ) and power transmittingand receiving devices (e.g., device 18 in FIG. 1 ) may includebatteries. These devices may operate in a power transmitting mode duringwhich wireless power is transmitted to an additional electronic device.To allow for user interface updates, role swaps within the wirelesscharging system, and/or to notify a user of an end of power transfer,the device in the power transmitting mode may transmit its battery stateof charge to the power receiving device using in-band communication(e.g., FSK modulation) using a coil while simultaneously transmittingwireless power to the power receiving device using the coil.

FIG. 11 is a top view of an illustrative wireless charging system havinga first device 202 (e.g., device 1) adjacent to a second device 204(e.g., device 2). In the example of FIG. 11 , device 1 is a cellulartelephone (which may be a power transmitting and receiving device or adedicated power receiving device) and device 2 is a battery case (whichmay be a power transmitting and receiving device or a dedicated powertransmitting device). These examples are merely illustrative. Ingeneral, device 1 and device 2 may be any type of device.

The battery case 204 may include a rectangular recess with a rear wallsurrounded by peripheral sidewalls and/or other suitable couplingstructures (straps, clips, a sleeve, corner pockets, etc.) that allowthe case to receive and couple to the device 202. The case mayoptionally include a front cover portion that is coupled to a rear coverpotion with flexible structures. The front cover portion may beconfigured to optionally cover a front face of device 202.

During operation, device 204 may operate in a power transmitting modeand device 202 may operate in a power receiving mode. While in thisconfiguration, device 204 may transmit its battery state of charge todevice 202. Device 204 may transmit the battery state of charge todevice 202 using a given wireless power coil and in-band communication(e.g., FSK modulation) while transmitting wireless power with the givenwireless power coil.

Device 202 may display battery charge status information 206 (sometimesreferred to as battery charge status, battery charge information,battery charge status indicator, etc.). The battery charge statusinformation 206 may represent a state of charge of the battery of device1 (device 202). Additionally, device 202 may display battery chargestatus information 208 (sometimes referred to as battery charge status,battery charge information, battery charge status indicator, etc.). Thebattery charge status information 208 may represent a state of charge ofthe battery of device 2 (device 204). Device 202 may display batterycharge status information 208 based on the battery charge statusinformation received from device 204 using in-band communication.

A battery-powered device in a power transmitting mode may transmit itsstate of charge in both a configuration phase (e.g., before a powertransfer phase) and during a power transfer phase. As shown inconnection with FIGS. 4 and 5 , a device in a power transmitting modemay transmit a capabilities packet (e.g., packet 108) that includesinformation on the state of charge of the battery of the powertransmitting device. This is an example of the state of chargeinformation (for the power transmitter's battery) being transmitted fromthe power transmitter to the power receiving device before a powertransfer phase (e.g., during a configuration phase).

In another example, the power transmitting device may transmit its stateof charge during wireless power transfer (e.g., in response to a queryfrom the power receiving device). FIG. 12 is a timing diagram showing anexample of this type. As shown, device 1 may send a state of chargequery 210 to device 2. The state of charge query may be sent usingin-band communications (e.g., ASK modulation) with a coil while the coilreceives wireless power from device 2.

In response to receiving the state of charge query, device 2 may sendits state of charge 212 to device 1. The state of charge may betransmitted from device 2 to device 1 using in-band communications(e.g., FSK modulation) with a coil while the coil transmits wirelesspower to device 1. In one example, the state of charge may betransmitted from device 2 to device 1 as part of a transmittercapabilities packet (e.g., packet 108 shown in FIG. 6 ) that alsoincludes information regarding the tether state of the powertransmitting device and the swap capabilities of the power transmittingdevice. In another example, the state of charge may be transmitted fromdevice 2 to device 1 in a dedicated packet that only includes the stateof charge of the transmitting device battery (e.g., the informationregarding the tether state and the swap capabilities may be omitted).

When device 1 receives the state of charge of the battery in device 2from device 2, device 1 may take appropriate action. As one example,device 1 may update its user interface that displays battery chargestatus information 208 for device 2. As another example, device 1 mayidentify that the state of charge of the battery of device 2 is below athreshold (e.g., 40%, 30%, 20%, 10%, 5%, less than 30%, less than 50%,between 1% and 30%, etc.). In response to identifying that the state ofcharge of the device 2 battery is below a threshold, device 1 mayinstruct device 2 to deliver less power (e.g., reduce the power transferlevel) or may instruct device 2 to cease delivering power entirely. Inaddition or instead, device 1 may output a user notification (e.g.,using one or more of audio feedback, visual feedback, and hapticfeedback) to notify the user that power transmission from device 2 todevice 1 will soon cease. As yet another example, device 1 may request arole swap so that device 2 switches to a power receiving mode and device1 switches to a power transmitting mode.

The example of FIG. 12 where device 2 transmits its battery's state ofcharge to device 1 in response to a query from device 1 is merelyillustrative. Device 2 may also transmit its battery's state of chargein response to identifying that the state of charge is below a threshold(e.g., 40%, 30%, 20%, 10%, 5%, less than 30%, less than 50%, between 1%and 30%, etc.), in response to device 1 being tethered to a wired powersource, in response to the state of charge of the battery of device 1being greater than the state of charge of the battery of device 2, inresponse to device 1 having a battery with a large storage capacity(e.g., larger storage capacity than the device 2 battery), etc. Device 2may also send a role swap or request to end power transfer in responseto identifying that the state of charge is below a threshold (e.g., 40%,30%, 20%, 10%, 5%, less than 30%, less than 50%, between 1% and 30%,etc.), in response to device 1 being tethered to a wired power source,in response to the state of charge of the battery of device 1 beinggreater than the state of charge of the battery of device 2, in responseto device 1 having a battery with a large storage capacity (e.g., largerstorage capacity than the device 2 battery), etc.

FIG. 13 is a flowchart of illustrative method steps for operating adevice in a power transmitting mode. Although the device in the powertransmitting mode may also be operable in a power receiving mode, thedevice will sometimes be referred to as a power transmitting device. Atstep 222, the power transmitting device may transmit informationidentifying that the power transmitting device has a battery usingin-band communication (e.g., FSK modulation). This information may betransmitted as part of a capabilities packet (as in FIG. 6 ) or as partof any other desired packet. Step 222 may occur during a configurationphase (e.g., before the power transfer phase). The power transmittingdevice may also optionally transmit additional wireless charginginformation during step 222. This optional information may include stateof charge information for the battery of the power transmitting device(as one example). The other information of packet 108 (e.g., tetherinformation, swap capabilities, etc.) may also be transmitted from thepower transmitting device to the power receiving device during step 222.

The power transmitting device may begin a power transfer phase duringwhich a coil is used to transfer wireless power to the power receivingdevice. Then, at step 224, the power transmitting device may receive astate of charge query from the power receiving device. The powertransmitting device may receive the state of charge query using in-bandcommunication (e.g., ASK demodulation) with the coil while power istransferred from the coil to the power receiving device.

In response to receiving the state of charge query, the powertransmitting device may transmit the state of charge for its battery tothe power receiving device at step 226. The power transmitting devicemay transmit the state of charge for its battery to the power receivingdevice using in-band communication (e.g., FSK modulation).

It should be noted that in some cases a power transmitting device thatdoes not include a battery may receive a state of charge query. In thesecases, the power transmitting device may respond with a predeterminedvalue indicating to the power receiving device that the powertransmitting device does not include a battery.

In one possible wireless communication scheme, the power receivingdevice may determine whether or not to cease wireless chargingoperations with the power transmitting device. In other words, the powerreceiving device determines based on the power transmitting devicebattery's state of charge (e.g., when the state of charge is below athreshold) whether or not to throttle or cease wireless charging. Inthis example, the power receiving device may optionally send the powertransmitting device an instruction to reduce a magnitude of powerdelivery or cease power transfer entirely.

In an alternate example, however, the power transmitting device maydetermine to throttle or cease wireless charging based on its own stateof charge (e.g., when the state of charge is below some threshold). Inthis example, the power transmitting device may optionally send thepower receiving device a message indicating that the state of charge islow and that the power transmitting device is planning to reduce amagnitude of power delivery or cease power transfer entirely. The powertransmitting device may reduce the maximum available power and send thisupdated capability information to the power receiving device.

The power transmitting device may transmit its state of charge to thepower receiving device in response to the state of charge being below athreshold (e.g., 40%, 30%, 20%, 10%, 5%, less than 30%, less than 50%,between 1% and 30%, between 1% and 10%, between 1% and 20%, etc.).Alternatively, the power transmitting device may transmit its state ofcharge to the power receiving device based on information indicatingthat the power receiving device is tethered to wired power, has a highstate of charge (e.g., higher than the threshold or higher than thetransmitter battery's state of charge), and/or has a large batterycapacity (as these conditions may be sufficient to prompt a role swap).

After a battery-powered wireless power transmitting device transmits itsstate of charge (e.g., as in step 226), the wireless power transmittingdevice may later change modes (if the device is capable of alsoreceiving wireless power). Numerous possible scenarios may lead to thebattery-powered transmitting device switching to a wireless powerreceiving mode. These scenarios include the power receiving device beingcoupled to a wired power source, the battery-powered transmitting devicebeing removed (decoupled) from the power receiving device andinductively coupled to a different coil of a different device that has awired power source (e.g., a charging mat), the state of charge of thebattery-powered transmitting device dropping below a threshold, etc.

FIG. 14 is a flowchart of illustrative method steps for operating adevice in a power receiving mode. Although the device in the powerreceiving mode may also be operable in a power transmitting mode, thedevice will sometimes be referred to as a power receiving device. Asshown, at step 232 the power receiving device may receive a messageindicative of the state of charge associated with a battery of the powertransmitting device. At the same time, the power receiving device may bereceiving wireless signals from the power transmitting device that aregenerated using the battery of the power transmitting device. The powerreceiving device may receive the message indicative of the state ofcharge using in-band communications (e.g., FSK demodulation).

The message indicative of the state of charge associated with thebattery of the power transmitting device may include the magnitude ofthe state of charge of the battery. In this example, the power receivingdevice may determine whether the state of charge is below a threshold atstep 234. The threshold may be any desired magnitude (e.g., 40%, 30%,20%, 10%, 5%, less than 30%, less than 50%, between 1% and 30%, between1% and 10%, between 1% and 20%, etc.). If the state of charge is abovethe threshold, the power receiving device may take no substantialaction. At a subsequent time, the power receiving device may optionallysend a query to the power transmitting device (e.g., using ASKmodulation) to obtain an updated state of charge of the battery of thepower transmitting device. If the state of charge is above thethreshold, the power receiving device may optionally update its userinterface (e.g., to present up-to-date battery charge status information208 in FIG. 11 ).

If the state of charge is below the threshold, the method may proceed tostep 236. As shown, at step 236 the power receiving device may present auser notification indicating an imminent or concurrent stop in wirelesspower transfer due to the state of charge of the battery of the powertransmitting device. For example, the user notification may be a visiblenotification including text, may include audio feedback, and/or mayinclude haptic feedback.

Also at step 236, the power receiving device may send an instruction tothe power transmitting device to reduce or cease power transferoperations. Alternatively, the power receiving device may allow thepower transmitting device to transmit all remaining power from thetransmitting device battery.

In some cases, the message indicative of the state of charge received atstep 232 may not explicitly include the magnitude of the state ofcharge. Instead, the message may be an ‘end power transfer’ packetindicating that power transfer will be imminently stopped. The end powertransfer packet may include a reason for the end of power transfer. Inthis example, the reason for the end power transfer packet may be thatthe state of charge of the battery in the power transmitting device hasdropped below a given threshold. In this case, the method may proceeddirectly to step 236 (as shown by the dashed arrow) to present the usernotification of the imminent end of power transfer.

The example described herein of a battery case transmitting its state ofcharge to a cellular telephone is merely illustrative. In anotherexample, two cellular telephones may be placed adjacent to each other,with one serving as a power transmitting device and one serving as apower receiving device. The devices may exchange state of chargeinformation as well as other charging information. In this context, abattery-powered cellular telephone may transmit the state of charge ofits battery to an additional cellular telephone using FSK modulation anda coil that is also simultaneously transmitting wireless power to theadditional cellular telephone.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. Control circuitry for an electronic device with awireless power coil, wherein the electronic device is operable in awireless charging system with an additional electronic device andwherein the control circuitry is configured to: using the wireless powercoil, transmit information to the additional electronic device thatidentifies the presence of a battery of the electronic device; using thewireless power coil and while transmitting wireless power signals to anadditional wireless power coil in the additional electronic device,receive a state of charge query from the additional electronic device;and responsive to receiving the state of charge query from theadditional electronic device, transmit a state of charge of the batteryto the additional electronic device using the wireless power coil. 2.The control circuitry of claim 1, wherein transmitting the state ofcharge of the battery to the additional electronic device using thewireless power coil comprises transmitting the state of charge of thebattery to the additional electronic device while transmitting, usingthe wireless power coil, the wireless power signals to the additionalwireless power coil in the additional electronic device.
 3. The controlcircuitry of claim 1, wherein transmitting the information to theadditional electronic device that identifies the presence of the batteryof the electronic device comprises transmitting the information to theadditional electronic device that identifies the presence of the batteryof the electronic device during a configuration phase, whereintransmitting the state of charge of the battery to the additionalelectronic device using the wireless power coil comprises transmittingthe state of charge of the battery to the additional electronic deviceusing the wireless power coil during a power transfer phase, and whereinthe configuration phase occurs before the power transfer phase.
 4. Thecontrol circuitry of claim 1, wherein receiving the state of chargequery from the additional electronic device comprises receiving thestate of charge query from the additional electronic device usingamplitude-shift keying communication.
 5. The control circuitry of claim4, wherein transmitting the state of charge of the battery to theadditional electronic device using the wireless power coil comprisestransmitting the state of charge of the battery to the additionalelectronic device using frequency-shift keying modulation.
 6. Thecontrol circuitry of claim 4, wherein transmitting the information tothe additional electronic device that identifies the presence of thebattery of the electronic device comprises transmitting the informationto the additional electronic device that identifies the presence of thebattery of the electronic device using frequency-shift keyingmodulation.
 7. The control circuitry of claim 1, wherein the controlcircuitry is further configured to: after transmitting the state ofcharge of the battery to the additional electronic device using thewireless power coil, receive a mode change request from the additionalelectronic device.
 8. The control circuitry of claim 7, wherein thecontrol circuitry is further configured to: in accordance with receivingthe mode change request from the additional electronic device, switchthe wireless power coil to a power receiving mode in which the wirelesspower coil receives wireless power signals.
 9. The control circuitry ofclaim 1, wherein the control circuitry is further configured to, aftertransmitting the state of charge of the battery to the additionalelectronic device: responsive to the additional electronic device beingconnected to a wired power source, switch the wireless power coil from atransmitting mode in which the wireless power coil transmits wirelesspower signals to a receiving mode in which the wireless power coilreceives wireless power signals.
 10. The control circuitry of claim 1,wherein the control circuitry is further configured to, aftertransmitting the state of charge of the battery to the additionalelectronic device: responsive to the electronic device being decoupledfrom the additional electronic device and coupled to a differentelectronic device, switch the wireless power coil from a transmittingmode in which the wireless power coil transmits wireless power signalsto a receiving mode in which the wireless power coil receives wirelesspower signals.
 11. The control circuitry of claim 1, whereintransmitting the state of charge of the battery to the additionalelectronic device using the wireless power coil comprises transmitting apacket to the additional electronic device using the wireless powercoil, wherein the packet comprises at least one bit that indicates thestate of charge of the battery, and wherein the packet comprises a firstbit that indicates whether the electronic device is capable of swappingmodes.
 12. The control circuitry of claim 11, wherein the packetcomprises a second bit that indicates whether the electronic device isconnected to an external power source.
 13. The control circuitry ofclaim 1, wherein the control circuitry is further configured to: aftertransmitting the state of charge of the battery to the additionalelectronic device using the wireless power coil, receive an instructionfrom the additional electronic device to deliver less power to theadditional electronic device.
 14. Control circuitry for an electronicdevice having a wireless power coil, wherein the electronic device isoperable in a wireless charging system with an additional electronicdevice and wherein the control circuitry is configured to: operate thewireless power coil in a transmitting mode in which the wireless powercoil transmits wireless power signals to an additional wireless powercoil of the additional electronic device; determine whether a state ofcharge of a battery of the electronic device is below a threshold; andwhile in the transmitting mode, use the wireless power coil to transmitthe state of charge of the battery to the additional wireless power coilin accordance with determining that the state of charge is below thethreshold.
 15. The control circuitry of claim 14, wherein the controlcircuitry is further configured to: after transmitting the state ofcharge of the battery to the additional wireless power coil, switch thewireless power coil from the transmitting mode to a receiving mode inwhich the wireless power coil receives wireless power signals.
 16. Thecontrol circuitry of claim 15, wherein switching the wireless power coilfrom the transmitting mode to the receiving mode in which the wirelesspower coil receives wireless power signals comprises switching thewireless power coil from the transmitting mode to the receiving moderesponsive to the additional electronic device being connected to awired power source.
 17. The control circuitry of claim 15, whereinswitching the wireless power coil from the transmitting mode to thereceiving mode in which the wireless power coil receives wireless powersignals comprises switching the wireless power coil from thetransmitting mode to the receiving mode responsive to the wireless powercoil being decoupled from the additional wireless power coil andinductively coupled to a different wireless power coil of a differentelectronic device.
 18. Control circuitry for an electronic device havinga wireless power coil, wherein the electronic device is operable in awireless charging system with an additional electronic device andwherein the control circuitry is configured to: operate the wirelesspower coil in a transmitting mode in which the wireless power coiltransmits wireless power signals to an additional wireless power coil ofthe additional electronic device; receive a first state of charge of afirst battery of the additional electronic device from the additionalelectronic device; compare the first state of charge to a second stateof charge of a second battery of the electronic device; and while in thetransmitting mode, use the wireless power coil to transmit the secondstate of charge of the second battery to the additional wireless powercoil in response to comparing the first state of charge and the secondstate of charge.
 19. The control circuitry of claim 18, wherein thecontrol circuitry is further configured to: after transmitting thesecond state of charge of the second battery to the additional wirelesspower coil, switch the wireless power coil from the transmitting mode toa receiving mode in which the wireless power coil receives wirelesspower signals; and after switching the wireless power coil from thetransmitting mode to the receiving mode, use the wireless power coil tosend information to the additional wireless power coil usingamplitude-shift keying modulation.
 20. The control circuitry of claim19, wherein the control circuitry is further configured to: aftersending the information to the additional wireless power coil usingamplitude-shift keying modulation, use the wireless power coil toreceive information from the additional wireless power coil usingfrequency-shift keying demodulation.